Impact of power control on the performance of space-time spreading systems with suboptimal detectors

We propose a transmit power allocation method in a multi-user MIMO downlink to improve the diversity gain achieved with suboptimal serial interference cancellation (SIC) detectors. Signals for individual users are transmitted at powers set according to the signal to interference and noise ratio (SINR) at each downlink receiver. As is well known, unequal power levels are beneficial to the SIC, which therefore performs better with the proposed signalling scheme than with equal power allocation. Naturally, second-order channel knowledge at the transmitter is required. The idea of transmitting symbols with unequal powers can also be used in a single-user MIMO system to achieve better diversity when using an SIC receiver for the purpose of reduced complexity.